The demand for development icons is huge, and thankfully this year has been a fairly productive year with new icon sets being freely released every other week. As you will see from the list below, they are all of high quality, some do have more flexibility than the others, and some do have limited numbers and options, but all are beautifully designed.
Anyway, all of the icons I have listed below have been designed specifically for web design, web development, web applications and blogging. And I am sure you will agree, they are amazing.

This icon pack comes packaged with 108 gray icons that can be easily customized within Photoshop and Fireworks. This Icon Pack ican be used in your personal and commercial projects, and can be used without attribution.

This free set includes 20 icons that you can use for both personal and commercial projects. Resell and distribution is not allowed. The icons are available in three different sizes: 16px, 32px, and 64px in 32-bits transparent.png format.

There are 25 scalable .aiformat icons in this set, which can be opened with any version above Illustrator 8.0. With earlier versions, you may loose some of the effects.
This set is licenced under Creative Commons License.

The package includes 30.png menu icons plus the additional source files for further customization.
All icons are distributed under a Creative Commons Attribution Share Alike license, so feel free to use them in any form in you projects or even remix them.

The icons are free for personal and commercial use, but the designers do require linking to there web site. The package contains 59 icons, available in four different sizes and are available in Windows, MAC and .png format.

The icons are available in.png, .icon and .icnsformat. They are free to use for both personal and commercial projects, including websites, templates and software. In total there are 100 icons at 64×64px.

There are 128 unique icons for apps, folders, settings, and the desktop. Each icon has two color variants, dark and light and each icon is available as a 128×128 .png or as a Windows .icon. There is also a .psd file included in the set for easy customization.

These iPhone UI icons are 24-bit .png images used as a mask to generate selected and unselected button states. Dimensions should be about 30×30 pixels for tab bar icons and about 20×20 pixels for toolbar and navigation icons.

All icons are completely free for both personal and commercial use. The icons are available in 4 different sizes (32×32 pixels, 48×48 pixels, 64×64 pixel, and 96×96 pixels) and come as 32-bit transparent .pngfiles. The icons are also available in vector format.

There are over 450 icons in this amazing set. The files are transparent .pngs, and the source files (.psd) are also available for download. The set is completely free and may be used for any private or commercial project without any restrictions whatsoever.

This is the fifth part of the Coquette free icon series. The icon set contains 50 high quality, free icons in these sizes: 16×16px, 32×32px, 48×48px, 64×64px and 128×128px and 32-bit transparency.png file format.

The icons are available in 5 different sizes (16×16px, 24×24px, 32×32px, 48×48px and 128×128px) and come as Windows ICO and 32-bit transparent .pngfiles. The icons are also available in vector format (Adobe Illustrator AI format).

The icon set includes 16 flags in two differenct style, normal style and rotated style. The raster icons come in three different sizes (32 pixels, 64 pixels and 128 pixels) and in 32-bit transparent .pngformat. Also the vector source file is included in the free set (Adobe Illustrator CS4 .ai format). The set is completely free for both personal and commercial use.

This set contains 20 icons for popular payment methods such as MasterCard, PayPal, Visa, American Express, Diner’s Club and much more… All icons are in .png format and come in three different sizes: big (130×80), small (80×49) and tiny (50×31).

Each icon in this set are in.png format and are supplied in 128px, 64px and 32px heights. There are two versions of each icon, one with curved edges (on a transparent background) and one with straight edges.

The RRZE (Regional Computing Centre Erlangen) has created a new icon set based on the Tango Desktop Project, which consists of an extensive and very uniformly created icon set. It focuses on Identity Management Systems, especially on user administration.
The RRZE Icon Set is licenced under a Creative Commons Licence.